Nicotine replacement using nicotine-containing chewing gum is one of the most promising treatment modalities to date for smoking addiction. However, much additional information is needed on how to increase the efficacy of nicotine polacrilex gum. Requisite investigations include the issue of appropriate dosages of nicotine polacrilex for heavily dependent smokers vs those low on dependence. Disappointing quit rates with heavy smokers given 2 mg seem to imply that larger dosages should be used for such smokers, but this issue has only recently begun to be studied. In addition, mechanisms whereby nicotine gum varying dosages may impact cessation rates need further study. Furthermore, we need to determine why the majority of smokers relapse even when provided nicotine gum. We have planned a multivariate study to address these issues. Six hundred smokers will be classified according to degree of dependence, high or low, at baseline, then randomly assigned to placebo gum, or 4 mg gum treatment. Treatment will consist of careful instruction in gum usage, counseling concerning how to quit and maintain abstinence, empathetic social support, and frequent follow-up to monitor progress. Subjects will be interviewed at baseline, 1 day post-cessation, 1 and 2 weeks post-cessation, then at 1, 3, 6, 9, and 12 months. We will also assess amount of gum used, amount of nicotine absorbed from gum use, liking for gum, and gum-related medical symptoms. Furthermore, we will evaluate degree of motivation, confidence, and effort expended, social supports available, proportion of smoker's in the subject's environment, and other factors hypothesized to be related to relapse or abstinence such as age, gender, and clinical depression. We will also measure self-reported withdrawal symptoms, and objective indices such as heart, blood pressure, and body weight. This study should provide a clear, definitive test of the hypothesis that increasing the dosage of nicotine polacrilex increases abstinence rates for dependent smokers. The study should also increase our understanding of why varying the dose of nicotine enhances (or fails to enhance) success rates, and our comprehension of factors which, either independently, or through their interactions with dosage and dependence, contribute to relapse and abstinence.